Electrochemistry, Vol. 70. No. 5, 2002



p308

Synthesis of Manganese Dioxide from Manganese Acetate and Ammonium Peroxiodisulfate for Lithium Primary Cells

Nobuaki MIYAMOTO,* Yuichi TAKADA, and Shiho MIURA

Department of Chemical Science and Engineering, Ariake National College of Technology (150, Higashihagio-machi,Omuta, Fukuoka 836-8585, Japan)

Received November 16, 2001 ; Accepted February 8, 2002

Manganese dioxides were prepared from heating manganese(II) acetate and ammonium peroxiodisulfate at 80-200Ž for 1 h. The yield of manganese dioxide decreased with the heating temperature („100Ž). After heating at 375Ž for 5 h in air, the formation of ƒΏ-MnO2 and ƒΐ-MnO2 phases was confirmed by X-ray diffraction. The specific surface areas of the products heated at 375Ž were 160-180m2 g-1. When the products were used as the cathode materials of lithium / manganese oxide cells, the discharge capacities of these cells were 281-287mAh g-1, which were higher than that of the cell using electrolytic manganese dioxide (210 mAh g-1). It was found that the product obtained by heating at 100Ž is hopeful to be used as a cathode material.



p311

Electroless Sn-Ag Alloy Plating by Displacement Reaction

Susumu ARAI,* Masanobu KUMAGAI, Norio KANEKO, and Naoyuki SHINOHARA

Department of Chemistry and Material Engineering, Faculty of Engineering, Shinshu University (4-17-1 Wakasato, Nagano 380-8553, Japan)

Received October 12, 2001 ; Accepted February 6, 2002

Electroless Sn-Ag alloy plating by the displacement reaction was investigated. A new bath containing potassium pyrophosphate, potassium iodide, metal salts, and thiourea was used. First, examinations of electroless Sn plating and electroless Ag plating were carried out, and then electroless Sn-Ag alloy plating was investigated. Anodic and cathodic polarizations were conducted to clarify the deposition mechanism. Sn-Ag alloy films with a range of Ag concentrations from 24 to 52 at.“ were obtained. The surface morphology of the films became smoother with decreasing Ag content. The Sn-Ag alloy films consisted of the ƒΐ-Sn phase and the ƒΓ (Ag3Sn) phase.



p316

Role of Chemisorbed Oxygen in Fixation of Palladium by an Activated Carbon, SCN-3M, from Aqueous Solution of its Complex Ion

Yuriy A. TARASENKO, Svitlana A. KOPYL, Vladimir F. LAPKO, Anatoliy A. LYSENKO, and Isao TOMIZUKA a

Institute of Sorption and Problems of Endoecology (13 General Naumov Str., Kiev, Ukraine)
aJapan Science and Technology Corporation

Received October 25, 2001 ; Accepted February 12, 2002

When the grains of an activated carbon (AC) came to contact with deaerated aqueous solution of tetrachloropalladate ions (TCPI), their surface was covered by a thin porous layer of metallic Pd. The deposited Pd remained unchanged for a long time on the grains. In the aerated solution of the same composition two different processes were observed. The first was deposition of a similar layer of metallic Pd on the external surface of the grains, followed by expansion and vanishing of a Pd-containing layer from the surface of the grains into their cores. The second was gradual fixation of Pd atoms on the external and the internal surface of the AC grains by mechanisms other than reduction of TCPI, likely by mechanisms of ion-exchange. The observed two processes were discussed with regards to the chemisorbed oxygen atoms on the external and the internal surface of the AC, which caused change of electrode potential as well as acquisition of ion-exchange ability.



p322

The Inhibitory Effects of Uracil Derivatives on Corrosion of Steel in Saturated Ca(OH)2 Solutions Containing NaCl

Norio NAKAYAMA

National Institute of Advanced Industrial Science and Technology (16-1 Onogawa, Tsukuba-shi, Ibaraki 305-8569, Japan)

Received December 13, 2001 ; Accepted January 25, 2002

The inhibitory effects of uracil and its derivatives on the corrosion of a steel used for reinforcement of concrete were investigated by polarization measurements in a saturated Ca(OH)2 solution containing 0.53 mol/dm3 NaCl at pH 12.5, which is a simulated concrete-pore solution, during short-term (7-day) experiments. The inhibition mechanisms were also investigated by surface analyses (FT-IR and XPS). Uracil, 5-nitrouracil, and 5-aminouracil inhibited the corrosion of steel. 5-Aminouracil was the most effective; its inhibition efficiency was more than 98“ at concentrations higher than 5.0~10-2 mol/dm3 in the solution. 5-Aminouracil was adsorbed onto steel surfaces in accordance with the Langmuir adsorption isotherm. In a NaOH solution containing 0.53 mol/dm3 NaCl at the same pH (12.5), 5-aminouracil did not exhibit any inhibitory effects, which suggests that calcium cations in the solution are indispensable for the inhibitory effect. The FT-IR spectra implied that 5-aminouracil was adsorbed onto iron oxides on the steel surfaces through the formation of a coordination bond with the amino group at position 5 and a coordination or a covalent bond with the carbon at position 6 of the pyrimidine ring. The XPS analysis showed that 5-aminouracil was adsorbed onto the steel surfaces along with calcium.



p329

Performance Evaluation of the Four-Electrode Type Measurement System for Ion-Transfer Voltammetry

Shigeo AOYAGI,a Masahki MATSUDAIRA,a Takahiro SUZUKI,a Hajime KATANO,b Shigeo SAWADA,c Hiroki HOTTA,d Seiko ICHIKAWA,d Takayasu SUGIHARA,d and Toshiyuki OSAKAI *d

aResearch & Development Department, Hokuto Denko Corporation (3028 Uenohara, Kamiechi, Atsugi-shi, Kanagawa 243-0801, Japan)
bDepartment of Bioscience, Fukui Prefectural University (Matsuoka-cho, Fukui 910-1195, Japan)
cDepartment of Chemistry, Faculty of Science and Technology, Kinki University (Higashiosaka, Osaka 577-8502, Japan)
dDepartment of Chemistry, Faculty of Science, Kobe University (Nada, Kobe 657-8501, Japan)

Received December 5, 2001 ; Accepted January 25, 2002

A four-electrode electrolytic cell for ion-transfer voltammetry was designed, in which a stationary oil/water interface can be renewed by pouring an aqueous solution from a reservoir. A new four-electrode potentiostat was also developed in order to achieve ideal iR compensation with a positive-feedback circuit. Performance evaluation of the four-electrode system was made through cyclic voltammetric, chronopotentiometric, and normal-pulse voltammetric measurements for the transfer of tetramethylammonium ion at the nitrobenzene/water interface. The developed potentiostat was found to show a proper response, even when nearly 100“ (at least 95“) iR compensation was achieved. A low-pass filter mounted in the potentiostat was successfully employed to reduce noise in current signal.



p334

Electrolytic Properties and Application to a Lithium Battery of Ternary Solvent Electrolytes with Ethylene Carbonate
|Dimethyl Carbonate|3-Methylsydnone and 3-Ethylsydnone

Yukio SASAKI,* Hayato MIURA, Kazuhiro TOMINAGA, and Noritoshi NANBU

Department of Applied Chemistry, Faculty of Engineering, Tokyo Institute of Polytechnics (1583 Iiyama, Atsugi, Kanagawa 243-0297, Japan)

Received September 5, 2001 ; Accepted February 21, 2002

The electrolytic conductivity and charge-discharge characteristics of the lithium electrode were examined in ternary solvent systems made up of an ethylene carbonate (EC)-dimethyl carbonate (DMC) equimolar binary mixture with 3-methylsydnone (3-MSD) and 3-ethylsydnone (3-ESD). The electrolytes used were LiClO4, LiPF6, LiBF4, LiCF3SO3, LiN(CF3SO2)2, and LiN(C2F5SO2)2. The order of the decrease in conductivity of the ternary solvent electrolytes at a mol ratio 0.5 of 3-MSD and 3-ESD was LiPF6„LiClO4„LiN(CF3SO2)2„LiN(C2F5SO2)2„LiBF4„LiCF3SO3. The 1 mol dm-3 LiN(CF3SO2)2 and LiN(C2F5SO2)2 electrolytes with large anions showed moderate conductivities of higher than 6-7mS cm-1 at a mol ratio 0.5 of 3-MSD and 3-ESD. Addition of 3-MSD and 3-ESD to the EC-DMC equimolar binary mixtures containing LiClO4, LiBF4, LiCF3SO3, and LiN(CF3SO2)2 is effective for raising lithium electrode cycling efficiency. We found by using scanning electron microscope (SEM) that the cycling efficiency is dependent on the dendrite formation and the morphology of the film formed on the Ni (working) electrode.


Copyright (c) The Electrochemical Society of Japan